1. More samples of the cell center (the microtubule organizing centers (MTOC) and the centrioles) were reconstructed from electron micrographs of serial sections of pigment cells of Holocentrus ascensionis. The method for three-dimensional reconstruction was further developed using the color capability of the computer graphics system to enhance parts of the cell center and a hidden-line algorithm was implemented. This center is implicated in forming and maintaining the cell shape and its filamentous systems. 2. The organization of the endoplasmic reticulum (ER) and the Golgi apparatus in arcuate nucleus neurons of the hypothalamus was studied. The outer surface of part of the ER, or whorl body (WB), was reconstructed from twenty sections. It was found that adjacent layers in the WB are equally spaced. We have initiated a study involving image analysis techniques to determine whether an intervening layer of sugar-like material is responsible for this constant gap. The significance of our findings is that it will allow us to follow the mechanism of ER shape changes and its relation to the Golgi apparatus. 3. Many sections of rat brain were digitized and processed for developing a single full stereotaxic representation of the whole brain. We have initiated the steps that will allow us to represent the projection of neurotransmitters, peptides and receptors in color in their respective locations. 4. We digitized many sections of mouse embryos at different stages of development. This reconstruction will be used to evaluate the effects of teratogens and to follow the migration of germ cells in embryos. Algorithms and programs were devised to digitize serial sections, to align them and reconstruct them into a single three dimensional image. These studies will further our understanding of how the cell acquires its shape, and organizes its organelles. The tissue studies will reveal new functional interrelationships in the brain and embryos.